Uptake and transport of superparamagnetic iron oxide nanoparticles through human brain capillary endothelial cells

The blood-brain barrier (BBB) formed by brain capillary endothelial cells (BCECs) constitutes a firm physical, chemical, and immunological barrier, making the brain accessible to only a few percent of potential drugs intended for treatment inside the central nervous system. With the purpose of overcoming the restraints of the BBB by allowing the transport of drugs, siRNA, or DNA into the brain, a novel approach is to use superparamagnetic iron oxide nanoparticles (SPIONs) as drug carriers. The aim of this study was to investigate the ability of fluorescent SPIONs to pass through human brain microvascular endothelial cells facilitated by an external magnet. The ability of SPIONs to penetrate the barrier was shown to be significantly stronger in the presence of an external magnetic force in an in vitro BBB model. Hence, particles added to the luminal side of the in vitro BBB model were found in astrocytes cocultured at a remote distance on the abluminal side, indicating that particles were transported through the barrier and taken up by astrocytes. Addition of the SPIONs to the culture medium did not negatively affect the viability of the endothelial cells. The magnetic force-mediated dragging of SPIONs through BCECs may denote a novel mechanism for the delivery of drugs to the brain.

Nanoparticle-derived non-viral genetic transfection at the blood-brain barrier to enable neuronal growth factor delivery by secretion from brain endothelium

Brain capillary endothelial cells form the blood-brain barrier (BBB) that denotes a major restraint for drug entry to the brain. The identification of many new targets to treat diseases in the brain demands novel thinking in drug design as new therapeutics could often be proteins and molecules of genetic origins like siRNA, miRNA and cDNA. Such molecules are otherwise prevented from entry into the brain unless encapsulated in drug carriers. The desirable entry of such large, hydrophilic molecules should be made by formulation of particular drug carriers that will enable their transport into the brain endothelium, or even through the endothelium and into the brain. This manuscript reviews the potential of different drug-carriers for therapy to the brain with respect to their targetability, biocompatibility, toxicity and biodegradability.

Differential chromatin association and nucleosome binding of the maize HMGA, HMGB, and SSRP1 proteins

In plants, chromosomal high mobility group (HMG) proteins have been identified in the HMGA family, containing A/T-hook DNA binding motifs, and in the HMGB family, containing an HMG-box DNA binding domain, that are considered architectural factors in chromatin. We have characterized the association of the HMGA protein, five different HMGB proteins, and the structure-specific recognition protein 1 (SSRP1) with maize chromatin by extraction experiments using NaCl, ethidium bromide, spermine, and distamycin A. The difference in the release of the proteins from chromatin by these reagents indicates that they are differentially associated with chromatin. This was confirmed by treatment of chromatin with micrococcal nuclease, demonstrating that the HMGA, HMGB2/3, and SSRP1 proteins are enriched in the highly nuclease-sensitive fraction of chromatin, which is likely to be transcriptionally competent. As examined by electrophoretic mobility shift analyses, the HMGA protein and the proteins containing an HMG domain (HMGB proteins and SSRP1) bind specifically to purified maize mononucleosomes that contain a histone octamer and approximately 165 bp of DNA. The mode of interaction with the nucleosomes differs for HMGA and HMGB proteins. In the case of the HMGB1 protein, the full-length protein is required for specific nucleosome binding, as the individual HMG-box DNA binding domain (which is sufficient for DNA interactions) interacts nonspecifically with the nucleosomes. Collectively, these findings indicate that HMGA, the various HMGB proteins, and SSPR1 are differentially associated with plant chromatin and may act as architectural factors in different nucleoprotein structures.

DNA-interactions and nuclear localisation of the chromosomal HMG domain protein SSRP1 from maize

The structure-specific recognition protein 1 (SSRP1) is a member of the protein family containing a high mobility group (HMG) domain DNA-binding motif. We have functionally characterised the 71.4 kDa Zm-SSRP1 protein from maize. The chromatin-associated Zm-SSRP1 is detected by immunoblot analysis in maize leaves, kernels and suspension culture cells, but not in roots. Mediated by its HMG domain, recombinant Zm-SSRP1 interacts structure-specifically with supercoiled DNA and DNA minicircles when compared with linear DNA. In linear duplex DNA, the protein does not recognise a specific sequence, but it binds preferentially to sequences containing the deformable dinucleotide TG, as demonstrated by a random oligonucleotide selection experiment. Zm-SSRP1 modulates DNA structure by bending the target sequence, since it promotes the circularisation of short DNA fragments in the presence of DNA ligase. Moreover, Zm-SSRP1 facilitates the formation of nucleoprotein structures, as measured using the bacterial site-specific beta-mediated recombination reaction. Analysis of the subcellular localisation of various SSRP1-GFP fusions revealed that, in contrast to HMG domain transcription factors, the nuclear localisation sequence of Zm-SSRP1 is situated within a 20-amino acid residue region adjacent to the HMG domain rather than within the DNA-binding domain. The results are discussed in the context of the likely function of SSRP1 proteins in transcription and replication.

Linker histones play a role in male meiosis and the development of pollen grains in tobacco

To examine the function of linker histone variants, we produced transgenic tobacco plants in which major somatic histone variants H1A and H1B were present at approximately 25% of their usual amounts in tobacco chromatin. The decrease in these major variants was accompanied by a compensatory increase in the four minor variants, namely, H1C to H1F. These minor variants are smaller and less highly charged than the major variants. This change offered a unique opportunity to examine the consequences to a plant of major remodeling of its chromatin set of linker histones. Plants with markedly altered proportions of H1 variants retained normal nucleosome spacing, but their chromosomes were less tightly packed than those of control plants. The transgenic plants grew normally but showed characteristic aberrations in flower development and were almost completely male sterile. These features correlated with changes in the temporal but not the spatial pattern of expression of developmental genes that could be linked to the abnormal flower phenotypes. Preceding these changes in flower morphology were strong aberrations in male gametogenesis. The earliest symptoms may have resulted from disturbances in correct pairing or segregation of homologous chromosomes during meiosis. No aberrations were observed during mitosis. We conclude that in plants, the physiological stoichiometry and distribution of linker histone variants are crucial for directing male meiosis and the subsequent development of functional pollen grains.